The invention relates to a method and an apparatus for the examination of structures with widths of several micrometers on membrane surfaces.
With the increasing miniaturization of the structures of microelectronic circuits and micromechanical components, the analysis of very fine structures (in the .mu.- and sub-.mu.-range) with a high resolution is gaining in technical importance.
In practice, electron spectroscopy has achieved good results with respect to surface analysis. The basic design of apparatuses used for electron spectroscopy is described in the publication by Wannberg, B., Gelius, U. and Siegbahn, K. "Design Principles in Electron Spectroscopy" in Journal of Physics E, Vol 7 (1974), P. 149-159. In this text, three basic possibilities are mentioned for generating the electrons to be examined. The electrons may be generated by means of an x-ray source, or by means of a UV-light source, by means of a primary electron beam on the sample surface.
Because of the good focussing capability of electron beams, the surface analysis of microstructures normally takes place by means of the Auger effect (electron-induced Auger electron spectroscopy, e.sup.- AES). The disadvantages of this method are that the structure to be examined is subjected to high stress which leads to numerous points of radiation damage in the sample. Further, the method cannot be used on insulating substances.
Both disadvantages are avoided if the triggering of the electrons takes place by means of x-rays (x-ray photoelectron spectroscopy, XPS). This method, at the same time, supplies information on the bonding condition on the surface of the solid.
However, x-rays cannot be focussed as easily as electron beams. For this reason, this method has a much poorer physical resolution capacity and is therefore not very suitable for the examination of very fine structures.
The resolution capacity of the XPS-method may be improved in that the x-rays are generated in a physically very limited area. For this purpose, a primary electron beam is focussed on the rear surface of a membrane which releases x-rays in the membrane. The released x-rays, which are emitted on the front surface of the membrane, represent a physically narrowly limited x-rays source. Because of the absorption of the x-rays in the membrane, thin membranes, i.e. on the order of several micrometers, must be used in this method. The local x-ray sources locally release photoelectrons on the membrane surface which are analyzed by means of spectrometers. Because of the low emission depth of the photoelectrons, only the uppermost atom layers are detected.
This type of a high-resolution XPS-method was described by J. Cazaux in "Microanalyse et Microscopie Photo-Electronique X: Principe et performances previsibles," Revue de Physique Appliquee, 1975, P. 263-280 and carried out by C. T. Hovland in "Scanning ESCA: A New Discussion for Electron Spectroscopy," Applied Physics Letters, Vol. 30, 1977, P. 274-275. In the case of this method, the photoelectrons triggered by the x-ray quanta can be accepted by the spectrometer only in the extension of the direction of the impinging primary electrons. This angular configuration cannot be implemented in commercially-available Auger probes. Special measuring apparatuses must therefore be constructed for the application of this method.